Chaotic dynamics in preheating after inflation

We study chaotic dynamics in preheating after inflation in which an inflaton is coupled to another scalar field chi through an interaction (1)/(2)g(2)phi(2)chi(2). We first estimate the size of the quasi-homogeneous field X at the beginning of reheating for large-field inflaton potentials V(phi) = V-0 phi(n) by evaluating the amplitude of the chi fluctuations on scales larger than the Hubble radius at the end of inflation. Parametric excitations of the field chi during preheating can give rise to chaos between two dynamical scalar fields. For the quartic potential (n = 4, V-0 = lambda/4) chaos actually occurs for g(2)/lambda < O(10) in a linear regime before which the backreaction of created particles becomes important. This analysis is supported by several different criteria for the existence of chaos. For the quadratic potential (n = 2), the signature of chaos is not found by the time at which the backreaction begins to work, similar to the case of the quartic potential with g(2)/lambda >> 1.